Chargers and other power supplies use transformers as a means of power conversion from alternating current (AC) to direct current (DC). Unfortunately, transformers do not lend themselves well to miniaturization. In a planar transformer, using a flex circuit patterned with metal forms the primary and secondary coils of the transformer. However, the limitations of the flex circuit manufacture can be quite troublesome. The limited thickness of the copper traces that can be plated or deposited onto the flex substrate in order to form the coils leads to high DC resistances of the coils themselves, translating into lower efficiencies of the transformer (10% lower in some cases). Additionally, because these substrates are very thin, they are difficult to handle and analyze. Furthermore, current transformer technologies typically require about 11 different layers, including adhesive layers and safety layers, to be stacked together. This abundance of layers is problematic with respect to the complexity of manufacturing and the level of cost.
What is needed in the art is a magnetics package that reduces the resistances of the coils, makes them easy to handle, and minimizes both the complexity and cost of manufacturing.